The permanent alteration of the hair color by the application of hair dyes is well known. In order to provide the consumer with the shade and the intensity of color desired, a complex chemical process is utilized. Permanent hair dyeing formulations typically comprise oxidative hair dye precursors, which can diffuse into the hair through the cuticle and into the cortex where they then react with each other and a suitable oxidizing agent to form the end dye molecules. Due to their larger size, the resultant molecules are unable to readily diffuse out of the hair during subsequent washing with water and/or detergents; hence delivering a consumer-desired permanency of color. This reaction typically takes place in an aggressive environment at approximately pH 10 in the presence of an alkalizing agent and an oxidizing agent. Typically an oxidizing composition (also called developer and/or oxidizing component) comprising the oxidizing agent and a dye composition (also called tint or dye component) comprising the alkalizing agent and if present the precursors dye molecules are mixed shortly before use. The consumer repeats this process regularly in order to maintain the desired hair color and shade and the intensity of color and to ensure continual, even coverage of the hair including coverage of new hair growth. Under application conditions some of the hair dye precursors currently used in permanent hair dyeing formulations may enter into contact with the skin of the consumer and may sometimes be responsible for skin allergy.
In order to try to overcome this problem, a new oxidative dye precursor has been developed, namely 2-methoxymethyl-p-phenylenediamine. Indeed, it has been found in previous communications and publications, that this new oxidative dye precursor shows a more favorable toxicological profile and has meanwhile been introduced as an industry standard as safe replacement for traditionally used paraphenylene diamines. While not wishing to be bound by theory it is also believed that the introduction of a methoxymethyl side chain into p-phenylenediamine may attenuate its sensitizing potency and reduce the risk of allergy induction (Toxicology and Applied Pharmacology, 274 (2014) 480-487). 2-methoxymethyl-p-phenylenediamine and its derivatives are defined according to the following formula:
wherein R1, R2, R3 and R4 are selected, independently from each other, from the group consisting of a C1-C6 alkylamino group, a C1-C6 alkylcyano group, a C1-C6 alkyl group, a C1-C6 alkyloxy group, a benzyl group, a hydrogen atom, a C1-C6 hydroxyalkyl group, or a C4-C6-polyhydroxyalkyl group, wherein the alkyl groups may be linear or branched.
Instead of using permanent hair dyeing compositions, it is possible to use temporary or semi-permanent hair dyeing formulations which comprise direct dyes. Some of the direct dyes which are currently used in these temporary or semi-permanent hair dyeing formulations may also sometimes be responsible for skin allergy. Therefore, there is still the need of providing direct dye compounds and compositions comprising these direct dye compounds which are characterized by a reduced sensitizing potency and therefore a reduced risk of allergy induction.
Furthermore, some of the direct dyes which are currently used in these temporary or semi-permanent hair dyeing formulations may also be sensitive to the action of oxidizing agents such as hydrogen peroxide which make them generally unusable in lightening direct dye compositions comprising an oxidizing agent in combination with an alkalizing agent. Therefore, there is also still the need of providing direct dye compounds that can be used in compositions comprising an oxidizing agent in combination with an alkalizing agent.
Finally, there is also the need of providing direct dye compounds and compositions comprising these direct dye compounds which can provide the hair with a yellow or orange colour.